1. Technical Field of the Invention
The present invention relates to promoting the toning of human skin by stimulating, via topical application thereto of at least one hydroxystilbene compound, the restructuring of the skin and/or mucous membranes, whether by stimulating the synthesis of collagen and/or stimulating the proliferation of the fibroblasts of the dermis.
This invention also relates to skin-toning compositions comprising at least one hydroxystilbene compound.
2. Description of the Prior Art
Human skin consists of two layers, namely, a superficial or upper layer, the epidermis, and a deep layer, the dermis.
The natural human epidermis is principally composed of three types of cells which are the keratinocytes, highly predominant, the melanocytes and the Langerhans' cells. Each of these cell types contributes, through its specific functions, to the essential role played by the skin.
The dermis provides a solid support for the epidermis. It is also its feeder layer. It consists mainly of fibroblasts and an extracellular matrix itself composed of various extracellular proteins, including among which are, in particular, collagen fibers, elastin and various glycoproteins. All of these extracellular species are synthesized by the fibroblast. Also present in the dermis are leukocytes, mastocytes or tissue macrophages. Finally, the dermis contains blood vessels and nerve fibers.
The fibroblast, by virtue of its activity in the synthesis of extracellular matrix proteins (proteoglycans, collagen fibers and other structural glycoproteins) is the primary constituent in the structural assembly of the dermis.
The collagen fibers are responsible for the solidity of the dermis. These are very resistant but sensitive to certain enzymes generally deemed collagenases. In the dermis, the collagen fibers consist of fibrils firmly attached to each other, thus forming more than ten types of different structures. The structure of the dermis is in large part due to the entanglement of the packed collagen fibers. The collagen fibers participate in the tonicity of the skin.
The collagen fibers are regularly renewed but this renewal decreases with age, which causes, in particular, a reduction in the thickness of the dermis.
It is also accepted that extrinsic factors such as ultraviolet radiation or tobacco smoke also have an adverse effect on the skin and on its collagen level.
However, various factors cause the degradation of collagen, with all the consequences which can be expected on the structure and/or firmness of the skin and/or mucous membranes.
Although very resistant, the collagen fibers are sensitive to certain enzymes, the collagenases. Degradation of the collagen fibers causes the appearance of flabby and wrinkled skin which humans, preferring the appearance of a smooth and firm skin, have always sought to combat.
Collagenases belong to the family of enzymes denominated metalloproteinases (MMPS) which are themselves members of a family of proteolytic enzymes (endoproteases) which contain a zinc atom coordinated with three cysteine residues and a methionine species in their active site and which degrade the macromolecular components of the extracellular matrix and the basal sheets at neutral pH (collagen, elastin, and the like).
Being very widely distributed in the human body, these enzymes are present, but weakly expressed, in normal physiological phenomena such as organ growth and tissue renewal.
The metalloproteinase family consists of several well-defined groups based on their resemblance in terms of structure and substrate specificity (see Woessner J. F., Faseb Journal, vol. 5, 2145 (1991)). Among these groups, exemplary are the collagenases intended for degrading fibrillar collagens (MMP-1 or interstitial collagenase, MMP-8 or neutrophil collagenase, MMP-13 or collagenase 3), gelatinases which degrade collagen type IV or any form of denatured collagen (MMP-2 or gelatinase A (72 kDa), MMP-9 or gelatinase B (92 kDa) stromelysins (MMP-3) whose broad activity spectrum applies to extracellular matrix proteins such as glycoproteins (fibronectin, laminin), proteoglycans, and the like, or, alternatively, membrane metalloproteinases. Prolonged exposure to ultraviolet radiation, particularly to UV-A and/or UV-B ultraviolet radiation, elicits the effect of stimulating the expression of collagenases, particularly of MMP-1. This constitutes one of the components of photoinduced skin aging.
Moreover, at menopause, the principal modifications regarding the dermis are a reduction in the collagen level and in the dermal thickness. This causes, in menopausal women, a reduction in the thickness of the skin. Women then experience a sensation of "dry skin" or of tight skin and a marked increase in surface fine lines and fine wrinkles is observed. The skin exhibits a rough appearance upon palpation. Finally, the skin exhibits a reduced suppleness.
It too is known that women gradually lose their collagen level yearly after menopause and that 30% of the overall level is lost in the first five years postmenopause.
The importance of the presence of collagen fibers in the skin and the importance of maintaining, or even increasing, the amount thereof, thus, are self-evident.
Serious need therefore continues to exist for active species/agents that maintain the level of collagen in the skin and maintain a smooth and firm appearance thereof.